1. Field of the Invention
The present invention relates to manufacturing processes for intraocular lenses (IOLs), tumbling processes used in the manufacture of molded IOLs and IOLs manufactured with the processes.
2. Related Art
Methods of molding articles from a moldable material, such as plastic, have been practiced for quite some time. A common problem associated with molding processes is the formation of excess material or flash on the molded article. Depending upon the type article formed in the molding process and the manner in which the article is used, the existence of excess material or flash can be undesirable.
Prior methods of removing flash from molded articles include such labor intensive processes as cutting the flash with a blade or scissors. However, such cutting methods can be extremely time consuming and expensive, especially when a large number of articles are being manufactured.
Methods of removing flash by tumbling the molded article in a rotatable tumbling container have been successfully practiced. For example, U.S. Pat. No. 2,084,427 to Boderson and U.S. Pat. No. 2,387,034 to Milano describe methods of making plastic articles, buttons in particular, which include steps of tumbling the articles to remove projections of excess material or flash. Similarly, U.S. Pat. No. 4,485,061 to Akhavi et al. describes a method of processing plastic filaments which includes "abrasive tumbling" to remove excess material.
A cold temperature tumbling process is described in U.S. Pat. No. 2,380,653 to Kopplin. According to this method, flash is removed from a molded article by tumbling the article in a rotatable container of dry ice and small objects, such as wooden pegs. The cold temperature resulting from the dry ice renders the flash material relatively brittle, such that the flash is more easily broken off of the article during the tumbling process.
U.S. Pat. No. 3,030,746 to Firestins, et al. describes a grinding and polishing method for optical glass, including glass lenses. The method includes a tumbling process wherein the glass articles are placed in a composition of a liquid, and abrasive and small pellets or media. The liquid is described as being water, glycerins, kerosine, light mineral oil and other organic liquids either alone or in combination; the abrasive is described as being garnet, corundum, boron carbide, cortz, aluminum oxide, emery or silicon carbide; and the media is described as being ceramic cones, plastic slugs, plastic molding, powder, limestone, synthetic aluminum oxide chips, maple shoe pegs, soft steel diagonals, felt, leather, corn cobs, cork or waxes.
Another example of a tumbling process used in the manufacture of optical lenses (including certain types of intraocular lenses) is described in U.S. Pat. No. 4,541,206 to Akhavi and U.S. Pat. No. 4,580,371, also to Akhavi. These patents describe a lens holder or fixture used for holding a lens in a process of rounding the edge of an optical lens. The process includes an "abrasive tumbling" step carried out with an "abrasive medium" 70 in a tumbler 72.
Prior methods of removing flash, such as described above, may be inadequate or impractical in the manufacture of certain types of intraocular lenses (IOLs). For example, certain modern IOLs are formed with a relatively soft, highly flexible material, such as a silicone material (e.g., Silicon "RMX-3 or RMX-3W), which is susceptible to chemical and/or physical changes when subjected to cold temperatures. Therefore, certain types of cryo-tumbling (or cold temperature tumbling) may be impractical in the manufacture of lenses made from such soft lens material. In addition, certain types of abrasive tumbling processes may be suitable for harder lens material, such as glass or polymethylmethacrylate (PMMA), but may not be suitable for softer lens material, such as Silicon RMX-3 or RMX-3W. Therefore, a need exists for a suitable process for removing flash from molded lens bodies made of a relatively soft lens material, such as Silicon RMX-3 or RMX-3W.